四川盆地关键构造变革期不整合特征及其油气地质意义

 随着震旦系-下寒武统天然气勘探取得重大发现,对古构造格局有了新的认识,该地质时期发育呈南北向展布的隆坳构造。桐湾期、加里东期、印支期为四川盆地3 期关键构造变革期,其不整合分析是构造演化研究的重要手段,因此有必要通过关键构造变革期不整合研究,分析构造变革对古构造演化的影响。基于钻井、野外露头、地震资料分析,并结合区域地质资料,探讨关键构造变革期不整合发育特征,研究震旦纪-早寒武世古构造演化及其对震旦系天然气成藏的影响。结果表明:1)3 期关键构造变革形成了震旦系-下寒武统(桐湾期)、中上寒武统-二叠系(加里东期)及上三叠统-侏罗系(印支期),7 个区域性不整合;2)不整合具有叠合性、迁移性特征,叠合性主要反映构造继承性,迁移性主要反映古构造的变迁过程,依据不整合发育特征,高石梯-磨溪构造区构造演化划分为发育期、调整期及稳定期3 个演化阶段;3)不整合与隆起区丘滩体叠加控制了震旦系岩溶储层发育,不整合面可作为油气运聚优势通道,不整合迁移性有助于分析古构造圈闭的形成与消亡。分析认为,关键构造变革期不整合特征分析对认识震旦纪-早寒武世隆坳构造后期演化及油气运聚具有重要意义。

Unconformity characteristics and its petroleum geological implication in key tectonic change stages,Sichuan Basin

With great discoveries of natural gas in the Sinian System- Lower Cambrian, new understanding of the paleotectonic framework has been formed. The uplift and depression structure is distributed in north-south trending in that geological time. Three key tectonic change stages are Tongwan Stage, Caledonian Period and Indo- Chinese Epoch. The analysis of unconformity characteristics is an important technique in the research of tectonic evolution. Therefore, analysis of unconformities of key tectonic change stages is helpful for further understanding their influence on paleotectonic evolution. Based on the analysis of drilling, outcrop, seismic data, combined with regional geological data, we discuss the unconformity characteristics and paleotectonic evolution in the Sinian Period-Early Cambrian and their influence on gas accumulation in the Sinian System. The results showed that: 1) Three key tectonic changes formed, which are the Sinian System-Lower Cambrian (Tongwanian), Upper Cambrian-Permian (Caledonian Period) and Upper Triassic-Jurassic (Indo-Chinese Epoch), seven regional unconformities; 2) The unconformity characteristics consist of superposition and migration. Superposition mainly reflects the structural inheritance, and migration mainly reflects the change processes of paleostructure. Tectonic evolution of the Gaoshiti-Moxi zone could be divided into stages of puberty, adjustment and stabilization on the basis of unconformity characteristics; 3) Superposition of unconformity and mound-beach system in uplift zone controls karst reservoir development in the Sinian System. Unconformable surfaces can be used for migration and accumulation channels for oil and gas. Unconformity migration is helpful for analyzing the formation and vanishment of paleotectonic traps. The analysis of unconformity characteristics in key tectonic change stages is significant for the later evolution and hydrocarbon migration of uplift and depression tectonic areas in Sinian Period-Early Cambrian.